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#Post#: 125--------------------------------------------------
The ideal head job
By: Fried Ape Date: November 18, 2014, 4:31 am
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The cylinder head on the NF is a typical old-fashioned design:
it is large and hemispherical, with two big valves set at a wide
angle. The valves are big and heavy with thick stems, so need
powerful springs to haul them closed.
As a result it is not unusual to find that the valve heads have
'tuliped' - they can can start to distort under the spring
pressure. The valve seats also get a hard time, and so do the
guides.
The easiest way to get more torque (power) out of the engine is
to raise the compression ratio. However, the only way to do this
is to raise the crown of the piston (trying to avoid the
valves). This results in a combustion space shaped like the skin
of half an orange and will need an even more extravagent
ignition advance than thee engine has as standard.
So I stole an idea from Dave Degens that he used on his 24-hour
racing Triumphs.
This means getting the sides of the combustion chamber welded-up
and milled to make the combustion space more like an oval
bathtub.
[URL=
HTML http://s21.photobucket.com/user/bancquo/media/Classic%20Bikes/Falcone%20Forum%20Stuff/Paul%20Friday%20uploads/Inside_zps42b9f1e8.jpg.html][IMG]http://i21.photobucket.com/albums/b298/bancquo/Classic%20Bikes/Falcone%20Forum%20Stuff/Paul%20Friday%20uploads/Inside_zps42b9f1e8.jpg[/img][/URL]
It leaves space for the valves but fills-in the two sides to
reduce the combustion space and to provide a bit of squish from
the piston.
While you are having this done (I used the Cylinder Head Shop),
get the head drilled and threaded for a second spark plug. This
can be fitted so that it is vertical with respect to the bore,
and comes out 'inside' the U of the rocker box.
[URL=
HTML http://s21.photobucket.com/user/bancquo/media/Classic%20Bikes/Falcone%20Forum%20Stuff/Paul%20Friday%20uploads/Outside_zps5adeff69.jpg.html][IMG]http://i21.photobucket.com/albums/b298/bancquo/Classic%20Bikes/Falcone%20Forum%20Stuff/Paul%20Friday%20uploads/Outside_zps5adeff69.jpg[/img][/URL]
[URL=
HTML http://s21.photobucket.com/user/bancquo/media/Classic%20Bikes/Falcone%20Forum%20Stuff/Paul%20Friday%20uploads/Head_zps87922414.jpg.html][IMG]http://i21.photobucket.com/albums/b298/bancquo/Classic%20Bikes/Falcone%20Forum%20Stuff/Paul%20Friday%20uploads/Head_zps87922414.jpg[/img][/URL]
The two plugs are easily fired together using a double-ended
Japanese ignition coil.
The last step, couresty of Len at the Cylinder Head Shop again,
is to replace the valves and springs with something more
athletic.
[URL=
HTML http://s21.photobucket.com/user/bancquo/media/Classic%20Bikes/Falcone%20Forum%20Stuff/Paul%20Friday%20uploads/Head006_zps34e9a147.jpg.html][IMG]http://i21.photobucket.com/albums/b298/bancquo/Classic%20Bikes/Falcone%20Forum%20Stuff/Paul%20Friday%20uploads/Head006_zps34e9a147.jpg[/img][/URL]
This shows a valve with an 8mm stem diameter and a pair of
lighter springs.
The end result is that the engine pulls even more like a train,
but is able to hold a decent speed on motorways and up hills.
It now pulls a higher gearing, with the rear sprocket reduced by
two teeth.
The carb will probably need a bit of rejetting, but it's not
that difficult.
Cheers
#Post#: 126--------------------------------------------------
Re: The ideal head job
By: banquo Date: November 18, 2014, 4:47 am
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Looks good Paul. Might be better to link to the pix on
Photobucket, as I'm pretty sure we have very limited upload
space on this free forum.
Was the head still like that when you sold the bike?
Edit: Pix now linked to Photobucket
#Post#: 127--------------------------------------------------
Re: The ideal head job
By: nick949 Date: November 18, 2014, 6:56 am
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Excellent stuff Paul - thanks.
Nick
#Post#: 131--------------------------------------------------
Re: The ideal head job
By: Bruno Date: November 18, 2014, 9:55 am
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Very nice.That combustion chamber shape looks similar to the
work Gerry Branch did (and still does) on Harley EVO engines.Had
the same work done on a soft tail I had.
#Post#: 142--------------------------------------------------
Re: The ideal head job
By: Fried Ape Date: November 19, 2014, 4:40 am
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"Was the head still like that when you sold the bike?"
Yes - new owner delighted. He rides out with someone else who
has a New Falcon. The modified engine and taller gearing means
that he can out-accelerate them and hold a decent 70-75mph speed
on motorways.
Pre modification I found that I often had to slipstream lorries
on motorways.
#Post#: 155--------------------------------------------------
Re: The ideal head job
By: KenJ Date: November 19, 2014, 5:40 am
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Good to see Paul on the new Forum. What that man doesn't know
about the NF.....?
Having bought Paul's bike, I can confirm that once I'd sorted
out the jetting, fitted a K&N filter and a free flowing exhaust
(it's certainly not a silencer) it goes like the clappers.
Running on the original 34 tooth rear sprocket, I was clocked at
90 mph by a friend following on a modern Triumph. It blew a head
gasket shortly after!
By doing plug chops, I ended up with a 140 main jet, which runs
slightly lean. One higher may be better, but haven't got one to
try. I had a few blown head gaskets, but now it's torqued to 40
lbs, no problems. While I had the head off on first inspection,
I took 2mm off the overall diameter of the push rods
(drumsticks) and matched in the tapers, also grinding down the
steel cups to match, while narrowing the lock nuts on the
rockers. With the lighter valves, the reciprocating weight of
the valve train has been greatly reduced, allowing a safer upper
rev limit. I've no idea what the engine was revving to, when I
was clocked at 90, but it was high.
With twin plugs, the timing can be retarded due to the shorter
time needed to burn the fuel. I read that Porsche engines were
retarded by 10 degrees, when switched to twin plugs, so aimed
towards that. On the NF, this equates to zero static timing. At
this, my NF really barks, being extremely loud. Advanced to 4
degrees static, seems to give a softer engine at tick over.
There is a definite power band, when the engine changes rapidly
from plodder to racer. To harness the extra power (??) I fitted
the shiny new 31 tooth rear sprocket in the spares kit, that
Paul included with the bike. The sprocket transformed the bike,
giving a usable first gear and motorway cruising speed of over
70 mph, with an overtaking speed of 85 mph readily on tap. I
have no desire to test the flat out speed on this gearing.
My early intention was to skim 10lb off the flywheel, but I like
the easy one swing start and slow tick over pace of the bike,
feeling that I have the best of both worlds at the moment. Once
the weight is taken off, it can't be put back on.
Did you get a measurement of the compression ratio Paul?
#Post#: 158--------------------------------------------------
Re: The ideal head job
By: Fried Ape Date: November 19, 2014, 5:47 am
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Ken,
great to hear from you and very pleased thatt he bike is working
well.
I never did get around to measuring the compression ratio.
However, next time you blow a head gasket(... !) fill it with
some oil or water to the joint line and tell me how much it
takes.
Cheers
#Post#: 171--------------------------------------------------
Re: The ideal head job
By: banquo Date: November 19, 2014, 6:53 am
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You've been busy on here Mr Ape... ;)
Thanks for all your efforts in uploading all the stuff. It's
much appreciated.
Don't you feel tempted to go out and get another one..??? 8)
#Post#: 173--------------------------------------------------
Re: The ideal head job
By: Fried Ape Date: November 19, 2014, 10:20 am
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Compression ratio....
So, the original engine is 6.85:1
If we assume that the additional welding added 15cc of metal,
that would make the new CR around 8.1:1
The amount of weld added is a guess - here are the numbers for
various amounts:
Weld CR:1
5cc 7.2
10cc 7.6
15cc 8.1
20cc 8.6
Ooh, and an important point - the second spark plug is a 10mm.
There isn't much room for anything bigger.
#Post#: 175--------------------------------------------------
Re: The ideal head job
By: banquo Date: November 19, 2014, 10:46 am
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Just as a matter of interest, I wonder how much the combustion
efficiency is affected by plug position, rather than by the
double spark?
Did you ever try running it with only the 10 mm plug, and
disconnecting the original?
I wonder if it would be worth sleeving down the original plug
thread to 10 mm, so the 2 plugs are the same?
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